Breast cancer is the second leading cause of death in women. While death rates have been declining in the last 20 years, these decreases are believed to be the result of increased awareness, improved treatment, and earlier detection through screening. While X-ray mammography is the first line of attack for breast cancer screening, it has its limitations, especially for high-risk women. Thus, high-risk women are generally screened using MRI. Given the success of MRI in the past few years, clinical trials are now evaluating the extension of MRI-based breast cancer screening programs to medium-risk women. In recent reports, evidence shows that breast cancers can be detected even with abbreviated (i.e. 3 minute) MRI exams. While MRI sensitivity in detecting breast lesions is very high, its specificity is lower. Specifically, between about 55%-70% of suspicious MRI lesions are benign on pathology reports. Consequently, women need to undergo biopsies to confirm or refute the positive screening results. Typically, a targeted ultrasound is done following the detection of an MRI positive lesion to determine if the lesion can be biopsied under ultrasound guidance. Unfortunately, a sonographic correlation can only be found for 23-89% of such lesions. Therefore, a good fraction of biopsy procedures need to be guided by MRI, or not be performed at all. Although MRI-guided breast biopsy systems are widely available, many radiologists prefer to biopsy with ultrasound, as this is perceived to be more easily performed. In addition, while 55% of the sites owning a whole-body scanner worldwide perform breast MRI, only 5% of these sites perform interventional procedures.
There are a number of reasons why MRI-guided biopsies are not more common. To better understand their shortcomings, the tools of the procedure are highlighted in FIG. 1, and described as follows. The biopsy setup 100 is depicted in FIG. 1 as an assembled biopsy setup (a) and as separate components (b).
While a woman patient is positioned supine on a breast coil, the breast to be biopsied is compressed between a coarse plastic grid 101 and an immobilization, or compression plate (e.g. behind the grid in the lower-most image of FIG. 1). The grid typically has openings 103 sized 2 cm×2 cm. Each of the grid openings accepts a sub-grid insert 105 which contains a matrix of 3×3 insertion locations 107. The woman is advanced in the MRI scanner, and a contrast agent is administered to localize the lesion. A fiducial marker on the coarse grid 101 is used to identify lesion position relative to the biopsy device. The biopsy location is then defined by the clinician. This may be a time-consuming step, as the screening and biopsy images may be acquired in different orientations. Moreover, the screening images are acquired with the breasts uncompressed, while the biopsy images are acquired with the breast compressed. The compression can limit perfusion, hence causing the suspicious lesion not to enhance anymore. Following lesion identification, software computes the entry position (i.e., coarse grid position and grid insert position) and lesion depth, and reports it on the computer screen in the scanner control room. Typically, given the single degree of freedom available for biopsy tool advancement, a single entry location is possible for a given lesion. At this point, the patient is removed from the magnet, while the compressed breast containing the lesion remains in a fixed position. The clinician enters the scanner room, identifies the entry location (i.e., coarse grid row and column, as well as grid insert row and column) and inserts a stylet 109 into an introducer 111, then into the grid insert 105, and then into the coarse grid 101. Once a particular grid entry point is chosen, a single degree of freedom is allowed for the biopsy device, which can only advance orthogonal, at right angles, to the grid plane. The introducer has depth markings, and a moveable, friction-fit ring 112 to control the depth of its insertion into the breast. The stylet is advanced to the approximately depth into the breast (defined manually by the setting of the friction-fit ring by the physician), then replaced with a plastic obturator 113. The medical team leaves the room and the patient is re-imaged to confirm if the tip of the obturator is at the location of the lesion. Assuming image confirmation, the patient is taken out of the magnet again, the obturator is replaced with the biopsy gun, and biopsy samples are taken (e.g., by rotating the biopsy gun multiple times). At the end of the procedure, the biopsy gun is replaced with the obturator, the patient is advanced to the scan position, and another image is acquired, for visual assessment of biopsy success.
Prior art techniques, such as that described above, make MRI-guided breast biopsy workflow cumbersome, resulting in a procedure completion time of 30-60 min. This utilizes a large fraction of MRI scanner time, numerous personnel (e.g., interventional radiologist, nurse and scanning technologist), and drives cost high. The MRI-guided biopsies are conducted without real-time guidance. Thus, lesions can only be visualized for ˜10 minutes after the contrast agent was injected, while the woman is inside the MRI magnet. The biopsies are performed, however, outside the MRI magnet, with the women on the MRI table. Accuracy is limited given the 6 mm (or 8 mm) distance between possible adjacent insertion points (and depending on whether the adjacent insertion points fall within the same opening of the coarse grid or not). See FIG. 1. Thus, this also limits the locations where the tip of the biopsy needle can reach. Larger than needed tissue volume is therefore extracted to sample at least a fraction of the enhanced lesion.
In comparison, core biopsies, as typically performed for breast lesions under ultrasound guidance, employ 11-18 gauge needles (with 14 gauge being typical) and extract about 4 samples/lesion (for about 80 mg total mass of extracted tissue); vacuum assisted biopsies for MRI-guided biopsies typically employ 9 gauge needles and extract about 8 samples/lesion (for a total mass of extracted tissue of about 1.5 g). The lack of real-time guidance, the limited number of entry points, and the orthogonal advancement requirement make it difficult for the clinician to access lesions requiring high accuracy, such as the ones close to silicone implants. In addition, lesions located outside of the compression grid (e.g., posterior) are very difficult to access with any kind of accuracy. Furthermore, large blood vessels cannot be avoided; thus, accidental puncture can lead to the creation of a hematoma(s) and morbidity to the patient. In fact, about 1.5% of MRI-guided biopsies are interrupted due to excessive bleeding. Assessment of the biopsy procedure is done at the end visually, with no quantitative tool available to confirm the fraction of the lesion removed. Furthermore, by the end of the procedure, the contrast agent may have already washed out, providing different contrast and slightly different geometry that renders this visual assessment inaccurate.
Given the shortcomings described above, cancers can be missed. In one study, follow-up MRI, after benign and imaging-histology concordant MRI-guided biopsies, has shown that 8-12% of targeted lesions were inadequately sampled; malignancy was ultimately diagnosed in 14-18% of these cases. Follow-up after benign and imaging-histology discordant biopsies indicated malignancies in 13-44% of the lesions initially diagnosed as benign. False negative rates as high as 11.7% were recently reported for MRI-guided biopsies.
To fulfill the true potential of breast MRI as the test with unparalleled sensitivity for breast cancer detection, a simple and accurate solution for MRI guided breast biopsies needs to be devised. Widespread acceptance and practice of these biopsies, as currently implemented, is not practical or economically feasible due to the time, expense and high level of skill associated with current workflow. Further, given the percentage of false negatives, inaccuracy is a significant concern. The lack of a simple solution for MRI-guided breast biopsies will ultimately stunt the growth of breast MRI as a screening modality, and will prevent many women from benefiting from this very sensitive test. A need exists to fundamentally simplify and increase the accuracy of MRI-guided breast biopsy procedures. The invention will address some shortcomings of present day MR-guided biopsy procedures, rendering the procedures shorter in duration, more accurate, and cheaper.